The present invention relates to surface scanning of parts and more particularly concerns improved scanning methods and apparatus to provide precise information concerning one or more of surface characteristics, configuration, orientation, discontinuity, and elevation, and provides detailed three-dimensional data of an object surface.
Our prior application describes scanning apparatus that identifies parts and measures surface detail by sensing intensity of light reflected from the part surface back along the axis of a rotating scanning beam that is directed to the part in a perpendicular scanning pattern. A scanning laser beam is projected from a rapidly spinning disc to a part mounted on a conveyor which moves the part across and through the circular scan pattern of the rotating beam. Thus, the beam traverses the part many times during one passage of the conveyor along a number of closely-spaced scan paths that cover the entire part surface. By sensing the beam position at one or more points in its circular scan and by sensing the conveyor position, a set of signals are generated that define the XY coordinates of the beam position at each of a number of points determined by a high frequency clock and the speed of beam rotation and conveyor travel. Correlating the timing of reflection intensity signals from the detector with the beam scan position signals provides data defining reflection intensity of the scanned object surface at each of a number of very closely-spaced points on the object surface. In effect, a two-dimensional picture of the object has been made and, in fact, can be displayed as such on a video screen.
A great deal of valuable information is rapidly and efficiently obtained with great precision with the use of the apparatus described in our prior application. Nevertheless, for many applications, including inspection and measurement, it is desirable to obtain elevation information in addition to the two-dimensional information previously obtainable.
Our prior application contemplates obtaining elevational information on the part by replacing the scanning laser with a laser distance measuring system employing interferometry and Droppler techniques. However, such a system is large, complex, expensive and difficult to mount on a rapidly spinning disc.
Optical triangulation techniques have been employed to determine elevation, but these have been static-type arrangements or used in systems that can be moved for measurement from one point to another only in limited fashions and at low speed. No such arrangements have been suggested for complete elevation mapping of an object surface.
Resolution of the information (e.g., the number and spacing of data points) provided by the apparatus of our prior invention depends in part on scanning speed, which is limited by physical limits on the speed of rotation of discs of a useful size. Time required for an entire scan will vary with required resolution and the limited scanning speed. Therefore, a trade-off between resolution and overall scan time may be required, although in many instances it is desired to maximize resolution and minimize scan time.
Accordingly, it is an object of the present invention to avoid the limitations of prior apparatus, to provide two-dimensional scanning of increased speed and resolution, and, in addition, to provide elevation information.